Well if there was a hand to hand death match between the two, yeah the small guy would have been at such a serious risk.
However there was no hand to hand death match. The big guy could have started one when he was nose to nose to the small guy with the gun on the porch. If the big guy was only willing to do violence he probably could have easily gotten the gun away and killed the little guy. But he was instead trying to shame the small guy and call his bluff...so the big guy was certainly risking his life, very foolishly so. But I saw no evidence the small guy's life was at risk for there was no evidence that the big guy intended to harm the small guy.
That is not how that clause works. If the landowner reasonably believes that engaging the trespasser would put them at risk of serious bodily injury or death, they can opt for deadly force and do not have to resort to hand to hand first.
When the trespasser is significantly larger than the landowner, it is generally accepted by the courts as more than enough reasonable belief. To say otherwise would require 5’0” 100lb women to go hand to hand with 6’5” 300lb men before they could use a gun, which is f***ing stupid. By the case law standard, the big meathead was automatically a threat of serious bodily injury or death by the obvious size and strength difference. Under Texas law, simply being an aggressive trespasser of his stature relative to the landowner was all that was required to satisfy that element of the law.
The inverse of this is why it is *not* legal to use deadly force to run those annoying Girl Scouts selling cookies door to door off your land - they’re not big enough to reasonably pose a threat of serious bodily harm or death to you. Your wallet and your pants size, maybe, but not you personally.